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Ammonia, a compound of nitrogen and hydrogen (NH\(_3\)), combusts with oxygen in the presence of a copper catalyst, forming nitrogen and water as products. This chemical reaction is an example of a combustion process, which releases energy as heat. When ammonia combusts, the reaction is exothermic, indicated by the negative sign of the enthalpy change (\(\Delta H\)). An exothermic reaction implies that energy is released during the reaction.

The chemical equation for the reaction of ammonia with oxygen is:
4 NH\(_3\))(g) + 3 O\(_2\))(g) → 2 N\(_2\))(g) + 6 H\(_2\)O(g)
Here, the reactants are ammonia and oxygen, and the products are nitrogen and water vapor. The copper catalyst speeds up the reaction without being consumed in the process.

• Ammonia: A common source of fuel in chemical reactions due to its hydrogen content.
• Oxygen: Combines with ammonia during combustion to facilitate the chemical reaction.
• Copper Catalyst: Lowers activation energy and increases the rate of reaction.

Understanding the basics of combustion reactions is crucial for calculating energy changes and predicting reaction outcomes.

To perform calculations related to chemical reactions, knowing the molar mass of the substances involved is crucial. The molar mass is the mass of one mole of a given element or compound. For ammonia (NH\(_3\)), the molar mass can be calculated by adding the atomic masses of nitrogen and hydrogen.

Ammonia consists of:

• Nitrogen (N): Atomic mass = 14 g/mol
• Hydrogen (H): Atomic mass = 1 g/mol (3 hydrogen atoms in ammonia)

The total molar mass of ammonia is calculated as follows:
\(1 \times 14 + 3 \times 1 = 17 \text{ g/mol}\)
This value is essential for converting mass to moles, which can then be used to find out the amount of substance involved in a reaction. Always double-check atomic masses and incorporate significant figures for accuracy in calculations.

Energy change in a reaction can be determined by examining the enthalpy change (\(\Delta H\)). In ammonia combustion, we are provided with an enthalpy change value for a specific amount of substance. It's necessary to adjust this value depending on how much of the reactant you are working with.

In this case, the enthalpy change for burning 4 moles of ammonia is given as \(-1267 \text{ kJ}\). To find the energy change for a different number of moles, such as for 35.8 g of ammonia, which amounts to 2.106 moles:

• Calculate the enthalpy change per mole of ammonia: \(\frac{-1267 \, \text{kJ}}{4 \, \text{moles}}\)
• Multiply this value with moles of ammonia (2.106 moles):
  \(2.106 \times \frac{-1267}{4} = -667.41 \, \text{kJ}\)

The result indicates the total heat change when 35.8 g of ammonia undergoes combustion. Practicing this calculation helps in understanding how energy transformations occur during chemical reactions, which is a fundamental concept in thermochemistry.